DESCRIPTION: The research proposed in this competitive renewal application will continue theoretical and experimental investigations of magnetic relaxation coupling, a crucial component of proton spin relaxation in tissue and other dynamically inhomogeneous systems of biological interest. Such coupling may be exploited to provide an additional mechanism for achieving altered magnetic resonance image contrast thereby permitting superimposition of structural and/or dynamic information about the solid components on the magnetic resonance behavior of the solvent water. Such protocols for the enhancement of image contrast are becoming increasingly useful in clinical radiology. Previous work, some of which is quite imaginative and novel, from the principal investigator's laboratory has provided a secure foundation for the proposed studies which depend in part on a mechanistic understanding of proton cross relaxation. Such insight has largely been obtained for purified protein systems in solution and gel states which have been appropriately modified to mimic magnetic relaxation occurring in tissue. Studies are proposed which fall into the following categories: (1) definition of the mechanisms important for magnetization transfer in tissue component systems more complex than isolated protein gels and protein solutions; (2) definition of water molecule and other solvent molecule binding site structures and measure solvent molecule lifetimes for buried solvent molecules; (3) measurement of the changes in amide hydrogen exchange rates in low molecular weight proteins in response to hydrostatic pressure and time dependent electromagnetic fields; (4) characterization of the relaxation and dynamics of molecules in restricted high surface area geometrically constrained environments.